A simple model of domestic PV systems and their integration with building loads

Photovoltaic systems can reduce the CO2 emissions associated with the consumption of electricity in dwellings. One key issue that affects both the economic case for home installation and the integration with the mains electricity grid is the match between the instantaneous production and demand for power. This initial study considers a sample of 10 dwellings which were monitored under the UK Government’s Photovoltaic Domestic Field Trial. A simple PV system model is introduced and used to examine the variations in the balance between the imported and exported electricity of the monitored households. There are cases where a large proportion of the electricity generated by a PV system is be used directly by the household and instead is exported to the mains electricity grid. The possibility of using the model explore the effects of PV system size on the import and export balance, and the benefits of sharing production and consumption between nearby dwellings, is discussed

National survey of summertime temperatures and overheating risk in English homes

This paper presents one of the first national scale studies of summertime temperatures in English dwellings. Living room and bedroom temperatures were recorded in 207 homes across the England during the cool summer of 2007. Data was also collected by face-to-face household interviews. Fourteen homes (7%) were observed to be heated for part or all of the analysis period (July to August). Based on the BSEN15251 adaptive thermal comfort model, the 193 free-running dwellings would, in general, to be considered as uncomfortably cool. Over 72% of living rooms and bedrooms had more than 5% of hours below the BSEN15251 Cat II lower threshold, with over 50% having more than 5% of hours below the Cat III threshold. Detached homes and those built before 1919 were significantly cooler (p<0.05) than those of other type and age. Static criteria revealed that, despite the cool summer, 21% of the bedrooms had more than 5% of night time hours over 26ºC; which is a recommended upper limit for bedrooms. The bedrooms of modern homes, i.e. those built after 1990 or with cavity walls, were significantly warmer (p<0.05). The bedrooms in homes built prior to 1919 were significantly cooler (p<0.05). The living rooms of flats were significantly warmer than the living rooms in the other dwelling types (p<0.05).The incidence of warm bedrooms in modern homes, even during a cool summer, is of concern, especially as there is a strong trend towards even better insulation standards in new homes and the energy-efficient retrofitting of existing homes

APPLICATION OF TABLET COMPUTERS IN A CAPSTONE DESIGN COURSE

ABSTRACT Tablet PCs look much like regular laptop computers, except their digitized screens can be swiveled around, folded over, and written on with a stylus. Instructors have recognized that this simple write-on feature gives them the opportunity to change the way in which they lecture in a classroom. This paper examines the application of tablet PCs outside of the lecture hall. Specifically, it describes the application of tablet computers to a final year capstone design course. Particular applications include the replacement of the traditional individual design notebook with a shared electronic notebook and enhancement of sketching as a communication tool. A description of the capstone course is given to provide a context for how the tablets were used. The impact of the tablet PCs is discussed and the results of a user survey are presented

A novel shading analysis method for PV systems using sun path plots and high resolution performance data

This paper presents a technique for identifying and quantifying shading losses in PV systems. Five minute interval monitored data from domestic UK PV systems is used to assess the effects of trees and other shading objects on annual energy generation. Poor performance is identified from the relationship between in-plane irradiance and performance ratio. Shading events are identified by plotting the occurrences of poor performance on a ‘sun path plot’ of solar azimuth and elevation axes. Poor performance which concentrates about particular sun positions is identified as shading. Once identified, the energy loss due to shading is quantified

Identifying trends in the use of domestic appliances from household electricity consumption measurements

Results are presented from a monitoring study of the electricity consumption of a sample of UK domestic buildings. Five-minutely average whole house power consumption was recorded for 72 dwellings at five sites over a 2-year monitoring period. The mean annual electricity consumption for the households increased significantly by 4.5% (t = 1.9; p < 0.05, one-tailed) from the first to the second year of monitoring. New techniques are developed which estimate the electricity consumption of different appliance groups, based on analysis of the five-minutely monitored data. The overall increase in electricity consumption is attributed to a 10.2% increase in the consumption of ‘standby’ appliances (such as televisions and consumer electronics) and a 4.7% increase in the consumption of ‘active’ appliance (such as lighting, kettles and electric showers). The consumption of different energy user groups (low, medium and high) is also investigated and low and high users are identified as contributing to the overall increase in consumption. The need for further investigation, such as quantitative and qualitative studies, to improve understanding in domestic electricity consumption is discussed

Development of a statistical model for the prediction of overheating in UK homes using descriptive time series analysis

Overheating risk in dwellings is often predicted using modelling techniques based on assumptions of heat gains, heat losses and heat storage. However, a simpler method is to use empirical data to predict internal temperatures in dwellings based on external climate data. The aim of this research is to use classical time series descriptive analysis and construct statistical models that allow the prediction of future internal temperatures based external weather data. Initial results from the analysis of a living room in a house show that the proposed method can successfully predict the risk of overheating based on four different overheating criteria

Measured internal temperatures in UK homes: a time series analysis and modelling approach

This paper presents an analysis of internal air temperatures measured hourly in the living rooms of 230 domestic buildings in the city of Leicester, UK. Time series analysis is used to identify the mechanisms that shape room temperatures, during the summertime period of July and August, in rooms that are neither mechanically heated nor cooled, and to develop empirical models of room temperatures for use in predicting future temperatures based on past measured values and on future weather conditions. Such models can enable overheating risk alerts for homeowners and public authorities to be more accurately estimated and targeted

Measured internal temperatures in UK homes: a time series analysis and modelling approach

This paper presents an analysis of internal air temperatures measured hourly in the living rooms of 10 domestic buildings in the city of Leicester, UK. Time series analysis is used to develop empirical models of room temperatures in rooms that are neither mechanically heated nor cooled, during the summertime period of July and August 2009. The models are used in predicting future temperatures based on past measured values. Such models can enable overheating risk alerts for homeowners and public authorities to be more accurately estimated and targeted

Variation of indoor temperatures and heating practices in UK dwellings

The UK government is committed to making significant reductions in CO2 emissions by 2050. To meet this target, a considerable reduction in energy consumption will be required from domestic dwellings and, in particular, space heating, which accounts for more than 50% of the energy used in the UK housing stock. Temperature monitoring studies in the UK have been undertaken, these can inform modellers of the variation in indoor temperatures throughout the housing stock. This information will allow energy modellers to better predict the indoor temperatures demanded by household occupants, and consequently improve the accuracy of energy predictions. This paper presents preliminary results from a large-scale city-wide survey of over 500 homes in Leicester, UK. Temperature measurements were recorded at hourly intervals in over 300 homes. Household data, including socio-demographic information, were collected for each household. This dataset is used to investigate the relationship between indoor temperatures and house type. The results confirm that house type is related to differences in indoor temperatures, but this relationship is not significant during heated periods. Further analysis is ongoing to identify how other social and technical factors relate to indoor temperatures